(1) Field of the Invention
The present invention relates to a carrier moving mechanism for a carrier of the type where teeth of two nuts are brought into contact with confronting side faces of the lead of a screw shaft, for example, a carrier of a printer having a printing head supported thereon, wherein occurrence of the backlash to be caused by wearing of the lead of the screw shaft and/or the nut teeth is prevented.
(2) Description of the Prior Art
A conventional carrier moving mechanism will now be described with reference to FIGS. 1 and 2 of the accompanying drawings. FIG. 1 is a sectional view of the carrier moving mechanism and FIG. 2 is a side view of the carrier moving mechanism. In FIGS. 1 and 2, reference numeral 10 represents a screw shaft having a lead 12, reference numeral 14 represents a first nut having teeth 16 to be engaged with the lead 12 of the screw shaft 10, reference numeral 18 represents a second nut having teeth 20 to be engaged with the lead 12 of the screw shaft 10, and reference numeral 22 represents a carrier. The first and second nuts 14 and 18 are secured by bolts 24.
In the carrier moving mechanism having the structure shown in FIGS. 1 and 2, the backlash is eliminated in the following manner.
First, rotation of the screw shaft 10 is restricted, and the first nut 14 is secured to the carrier 22 by the bolts 24 so that the teeth 16 of the first nut 14 are brought into contact with one side face of the lead 12 of the screw shaft 10. Then, in the same manner as described above, the second nut 18 is secured to the carrier 22 by the bolts 24 so that the teeth 20 of the second nut 18 are brought into contact with the other side face of the lead 12 of the screw shaft 10.
If the first and second nuts 14 and 18 are thus attached to the carrier 22 so that the teeth of both the nuts 14 and 18 are brought into contact with both the side faces of the lead 12 of the screw shaft 10, respectively, the backlash can be eliminated.
In the carrier moving mechanism having the above-mentioned structure, however, if the carrier moving mechanism is used for a long time and the teeth of both the nuts and/or both the side faces of the lead of the screw shaft wear away, the backlash is caused according to the degree of wearing and re-adjustment should be performed. This is the fatal defect of the conventional carrier moving mechanism.